Multiplication of M. leprae has been obtained in vitro, and continued for nine passages at 30-60 day intervals. Best numbers per milliliter have been disappointing, leveling off at 1X10(6) - 1X10(7) per milliliter. It may be necessary to develop a continuous growth, large volume fermentor system to acquire milligram or gram amounts of wet or dry growth. Growth adjuvants are being used in an attempt to increase the growth rate as well as the cell harvest. A new species of mycobacterium, an "armadillo-derived mycobacterium" (ADM), has also grown out. We can quickly differentiate it from M. leprae by pyridine decolorization, which renders M. leprae, non-acid-fast. The ADM has now been fully characterized. According to physiological, genetic, and antigenic studies, it is a new species. Final experiments on the in vitro culture of Mycobacterium leprae are delayed. Scott Franzblau of the Hansen's disease center at Carville is a collaborator in this study. He has been supplying us with M. leprae cells purified from foot pad infection in the nude mouse. He also performs definitive tests for the species. We have access to M. leprae material from infected armadillos (the liver). Armadillo-derived M. leprae always has an admixture of armadillo-derived mycobacteria, or ADM. There are about twenty species of these, which have not been given names. The ADM overgrow M. leprae in our culture technique. Scott Franzblau's M. leprae infected nude mouse colony was recently wiped out with an epizootic. These mice take a year to develop infections. We must wait this long to finish out our experiments.